Dental restorative composite

ABSTRACT

The present invention provides a resin-based dental restorative that exhibits high condensability, low volumetric shrinkage and low shrinkage stress. To this end, one or more of a rheological modifier, dispersant and fluorocopolymer are mixed with a methacrylate resin and a fine mineral filler in amounts effective to improve the condensability of the resulting composite to achieve amalgam-like condensation, to reduce the volumetric shrinkage to less than about 2% during polymerization, to improve wear resistance, and to provide a composite with generally improved physical properties.

FIELD OF THE INVENTION

This invention relates to resin-based dental restoratives, and morespecifically to restorative compositions that exhibit highcondensability, low volumetric shrinkage and improved wear/abrasionresistance.

BACKGROUND OF THE INVENTION

Posterior and anterior tooth restoration is typically accomplished byexcavating a tooth that has decayed or is otherwise in need of repair toform a cavity. This cavity is filled with a paste material, which isthen compacted and shaped to conform to the original contour of thetooth. The paste is then hardened, typically by exposure to actiniclight. The paste material is a tooth colored, packable, light curable,polymerizable restorative composition comprising a highly filledmaterial.

Posterior tooth restorations, especially the Class II type, require theuse of a matrix band for proper application of a restorative. Therestorative has to be condensable. That is, as it is packed into thecavity of a tooth surrounded by a matrix band, the restorative mustdeform the matrix band in such a way that the original tooth contour isachieved. In addition, proper deformation of the matrix band leads toappropriate contact with the adjacent teeth.

Up to now, the only type of restorative having adequate rheologicalproperties for use with a matrix band has been amalgam. Amalgams havebeen employed as restoratives for this purpose for a long time and theyare known to have good wear characteristics, good marginal quality overtime due to buildup of corrosion products at the border of therestoration and a small coefficient of thermal expansion. The metalliccolor, however, is a drawback for their use as is the uncertainty of thebiological interactions of the metallic components of dental amalgams.

Tooth colored dental restorative composites are usually composed ofdispersions of glass filler particles below 50 gm in methacrylate-typemonomer resin. Splintered pre-polymerized particles, which are groundsuspensions of silica in pre-polymerized dental resins, may also beused. Additives such as pigments, initiators and stabilizers have alsobeen used in these types of composites. Because the glass particlesurface is generally hydrophilic, and because it is necessary to make itcompatible with the resin for mixing, the glass filler is treated with asilane to render its surface hydrophobic. The silane-treated filler isthen mixed with the resin at a proportion (load) to give a paste with aconsistency considered usable, that is to allow the paste to be shapedwithout it flowing under its own weight during typical use. This pasteis then placed on the tooth to be restored, shaped and cured to ahardened mass by chemical or photochemical initiation of polymerization.After curing, the mass has properties close to the structure of a tooth.

Although it has been found that increasing the load of a resin-basedcomposite leads to higher viscosity, amalgam-like condensability has notyet been achieved. There is thus a need in the dental profession to havea resin-based restorative that is condensable and compatible with theuse of a matrix band.

As stated previously, the resins typically used in dental restorativecompositions are mostly comprised of dimethacrylate monomers. Thesemonomers vitrify quickly upon initiation of polymerization bycrosslinking. The added glass particles after polymerization give ahigher modulus to the system and reduce crack propagation by dispersionreinforcement.

A significant disadvantage in the use of methacrylate resin-basedrestorative composites is that they shrink significantly after cure. Forexample, a modern hybrid composite shrinks approximately 3% after cure.This shrinkage leads to further tooth decay because bacterialinfiltration is possible. To address the problem of tooth decay,adhesives are used to coat the tooth surface to be restored before theapplication of the composite. The shrinkage stress during the initialphase of the vitrification process, however, is significant and on theorder of 1 MPa or higher during the first 20 seconds of light exposurefor a light cure composite. This initial stress development compromisesthe performance of the adhesive. So even with the use of an adhesive,significant marginal breakdown can occur, leading to bacterialinfiltration. This process is defined as microleakage and is usuallymeasured by dye penetration methods. Thus, there is also a need to makeavailable to the dental profession a resin-based composite that hasreduced volumetric shrinkage and shrinkage stress.

The coefficient of thermal expansion of the glass fillers used inresin-based composites is much closer to tooth structure than that ofthe resins. So it is desirable to limit the amount of the resin in adental composite and maximize the amount of filler material. The mainfactor limiting the volume fraction (load) of the inorganic filler inhighly filled suspensions is particle-particle interactions.Dispersants, through their ability to reduce interactions betweenparticles can improve the flow (reduce the viscosity) of the suspension,therefore allowing a higher load. Dispersants in non-aqueous systemsreduce particle interactions by a steric stabilization mechanism. Alayer of the dispersant is adsorbed on the surface of the particleskeeping them apart from one another, reducing the viscosity. Thedispersant structure must contain a chain that allows for stericstabilization in the resin and it also must be strongly adsorbed on theparticle surface. There is thus a further need to provide a dispersantthat will be effective with a non-aqueous, highly filled suspensioncontaining polymerizable groups for use in a dental restoration.

An additional critical area needing improvement in dental restorationsis the wear and abrasion resistance of polymeric restorativecompositions. For posterior restorations, the main wear mechanism isgenerally classified as the three body type, involving food bolus. Foranterior restorations, wear is generally classified as the two bodytype, involving toothbrush abrasion, for example. Wear is caused by theheterogeneous nature of dental composites, occurring mostly through"plucking" of the filler particles from the surface followed by abrasionof the softer resin phase. Because wear in these systems is highlydependant on friction, friction reducing additives are expected toimprove abrasion resistance. For example, in Temin U.S. Pat. No.4,197,234, polytetrafluoroethylene powder or another similarpolyfluorocarbon resin or polyfluorochlorocarbon resin is added forimprovement of abrasion resistance in a chemically cured dentalcomposite. The polytetrafluoroethylene additive or other similaradditives, however, also act as an opacifying agent, making therestoration nonaesthetic. In other words, the color of the restorationdoes not blend sufficiently with the surrounding dentition. In addition,when the opacity is high, light cure initiation cannot be used.Similarly, Fellman et al. U.S. Pat. No. 4,433,958 describes the use ofseveral fluoropolymers as solid particulate insoluble in the liquidmonomer system in dental restorative formulations. Again, highly opaquematerials are obtained. There is thus an additional need to provide adental restorative composite with superior wear and abrasion resistancein both posterior and anterior applications, without causing undueopacity in the restorative.

In summary, the dental profession is in need of a dental restorativethat has improved shrinkage properties, higher load capabilities andsuperior wear and abrasion resistance, and that is condensable andcompatible with the use of a matrix band.

SUMMARY OF THE INVENTION

The present invention provides a resin-based dental restorative thatexhibits one or more of the following properties: high condensability,low volumetric shrinkage, low shrinkage stress, higher loading, lowercoefficient of thermal expansion, and high wear and abrasion resistance.In its broadest form, the dental restorative composition of the presentinvention includes (1) a polymerizable (meth)acrylic monomer; (2)filler; and (3) one or more of the following additives: a Theologicalmodifier in an amount effective to reduce the volumetric shrinkage ofthe dental restorative during polymerization/curing; a phosphate-baseddispersant; and a fluorocopolymer that is soluble in (meth)acrylateresin.

Suitable rheological modifiers for use in the present invention include,among others, the following two types of compounds:

(1) a hydroxyfunctional polycarboxylic acid amide according to theformula ##STR1## wherein the symbols have the following meanings:R=aliphatic hydrocarbon groups having 6 to 60 carbon atoms, or aromatichydrocarbon groups having ; to 20 carbon atoms, or aliphatic oraliphatic/aromatic hydrocarbon radicals having 6 to 150 carbon atomswhich are interrupted by 2, 4, 6 or 8 carboxamide groups, or aliphatichydrocarbon radicals having 4 to 150 carbon atoms which are interruptedby 2 to 75 --O-- (oxygen) groups;

R'=H, or C₁ to C₄ alkyl, or --Z'--(Q)_(y) --(OH)_(x) ;

x=1 to 3;

y=0 or 1;

Z=an alkylene radical having 2 to 6 carbon atoms;

Z'=an alkylene radical which is identical to or different from Z, having2 to 6 carbon atoms;

Q=an aliphatic hydrocarbon radical having 2 to 200 carbon atoms, whichis linked via --O-- or ##STR2## to Z or Z' and is interrupted by zero to99 oxygen atoms and/or carboxylic acid ester groups; and

n=2 to 3; and

(2) the reaction product of:

(a) from about 15 to 75 parts by weight of one or more liquidpolyalkoxylated nitrogen-containing compounds containing more than onehydroxyl group and which also contain a pendant aliphatic radical of 6to 40 carbon atoms selected from the group consisting of tertiary aminesand amides of secondary amines;

(b) from about 8 to 90 parts by weight of one or more polycarboxylicacids; and

(c) from about 0.5 to 20 parts by weight of one or more liquid diaminesof a weight average molecular weight of about 2000 or less,

wherein the reaction is continued until the acid value is within therange of 5 to 14 and the amine value is within the range of 42 to 84.

It has been found that the inclusion of either of the above rheologicalmodifiers in the resin and filler composition of the present inventionimproves the condensability and shrinkage properties of the resultingcomposite. By way of example, but not limitation, if the first mentionedmodifier is used it is preferably present in an amount of about 0.1 toabout 0.7 weight percent, and if the second modifier is used it ispreferably added in an amount of about 0.1 to about 1.5 weight percentof the total mixture.

Suitable phosphate-based dispersants for use in the present inventioninclude, among others, the following types of compounds:

(1) a phosphoric acid ester according to the formula ##STR3## whereinn=5 to 10 and m-1 to 20; and (2) a phosphoric acid ester according tothe formula ##STR4## wherein R is a (meth)acrylate group radical. R ispreferably one of the following radicals: oxyethyl methacryloyl-,oxyethyl acryloyl-, polyoxypropyl methacryloyl-, glyceryldimethacryloyl-, and dipentaerythritol pentaacryloyl-. The inclusion ofeither of the above types of dispersants or a combination thereof in theresin and filler composition of the present invention increases thefiller loading, which results in reduced shrinkage, a lower coefficientof thermal expansion and generally improved physical properties. Thedispersant is preferably present in an amount of 5 weight percent orless of the total mixture.

One suitable fluorocopolymer for use in the present invention is solublein (meth)acrylate resins and is comprised of about 40-60 mole percentfluoroolefin units, about 5-45 mole percent cyclohexyl vinyl etherunits, about 5-45 mole percent alkyl vinyl ether units and about 3-15mole percent hydroxyalkyl vinyl ether units. The inclusion of this typeof fluorocopolymer reduces the wear of the composite material. Thefluorocopolymer is preferably present in an amount of 10 weight percentor less of the total mixture.

There is thus provided a dental restorative having improved thixotropicand physical properties and improved wear resistance. These and otherobjects and advantages of the present invention shall become moreapparent from the description of the preferred embodiments and theexamples.

DETAILED DESCRIPTION

In connection with the present invention, it has been discovered that a)the addition of a suitable rheological modifier to a (meth)acrylateresin-based restorative composite improves the condensability andshrinkage properties of the resulting composite, without negativelyimpacting other critical properties; b) the addition of a suitabledispersant of the phosphoric acid ester type increases the fillerloading, and after curing provides a composite with reduced shrinkagecharacteristics; c) the addition of a suitable fluorocopolymer reducesthe wear of the composite without negatively impacting physical andaesthetic properties; and d) the addition of a combination of two ormore of a suitable rheological modifier, dispersant and fluorocopolymerprovides a dental restorative composite with improved condensability,shrinkage, wear, filler load and other physical and aestheticproperties.

Dental Restorative Composite with Rheological Modifier

Ordinarily, the restoration of posterior teeth, in particular Class IIrestoration, involves one or more side surfaces in addition to the topsurface of the tooth. After preparation of the cavity, a matrix band isplaced. The matrix band is a thin, malleable metal or plastic sheetdesigned to fit around the side surfaces of the tooth and designed to becapable of being tightened. Tightening the matrix band results inintimate contact with said tooth surfaces. Manipulation of the matrixband with dental instruments may then be necessary to achieve theoriginal tooth contour. The filing of the tooth is accomplished by anopening at the top surface. When the tooth is filled with amalgam, theamalgam is condensed (compacted) in such a way as to deform the matrixband further to give a better approximation of the original contour ofthe tooth. Heretofore, this type of deformation has not been possiblewith previously available resin-based composites even though they havebeen recommended for use in posterior tooth restoration. It is believedthat only by using the materials described in the present invention isamalgam-like condensation possible. This is accomplished by the additionof a rheological modifier to the resin and filler mixture. While variousrheological modifiers known for non-dental applications were tested foruse in dental restoratives of the present invention, it was found thatonly certain such modifiers provide the desired properties of increasedcondensability, lower volumetric shrinkage and reduced shrinkage stress:

One such modifier is Formula (1): a hydroxyfunctional polycarboxylicacid amide according to the formula ##STR5## wherein the symbols havethe following meanings: R=aliphatic hydrocarbon groups having 6 to 60carbon atoms, or aromatic hydrocarbon groups having 6 to 20 carbonatoms, or aliphatic or aliphatic/aromatic hydrocarbon radicals having 6to 150 carbon atoms which are interrupted by 2, 4, 6 or 8 carboxamidegroups, or aliphatic hydrocarbon radicals having 4 to 150 carbon atomswhich are interrupted by 2 to 75 --O-- (oxygen) groups;

R'=H, or C₁ to C₄ alkyl, or --Z'--(Q)_(y) --(OH)_(x) ;

x=1 to 3;

y=0 or 1;

Z=an alkylene radical having 2 to 6 carbon atoms;

Z'=an alkylene radical which is identical to or different from Z, having2 to 6 carbon atoms;

Q=an aliphatic hydrocarbon radical having 2 to 200 carbon atoms, whichis linked via --O-- or ##STR6## to Z or Z' and is interrupted by zero to99 oxygen atoms and/or carboxylic acid ester groups; and

n=2 to 3; and

Another such modifier is Formula (2): the reaction product of:

(a) from about 15 to 75 parts by weight of one or more liquidpolyalkoxylated nitrogen-containing compounds containing more than onehydroxyl group and which also contain a pendant aliphatic radical of 6to 40 carbon atoms selected from the group consisting of tertiary aminesand amides of secondary amines;

(b) from about 8 to 90 parts by weight of one or more polycarboxylicacids; and

(c) from about 0.5 to 20 parts by weight of one or more liquid diaminesof a weight average molecular weight of about 2000 or less,

wherein the reaction is continued until the acid value is within therange of 5 to 14 and the amine value is within the range of 42 to 84.

It is believed that the Formula 1 modifier may be obtained from BYKChemie USA, Wallingford, Conn. under the trade name BYK®-405. TheFormula 2 modifier, it is believed, may be obtained from RheoxCorporation, Hightstown, N.J. under the trade name Thixatrol® VF-10.Either modifier has the effect of providing pseudoplastic andthixotropic properties to the composite pastes. These rheologicalmodifiers and their thixotropic properties are described in U.S. Pat.Nos. 4,857,111 and 5,536,871, respectively, the entire disclosures ofwhich are incorporated herein by reference. The condensable nature ofthe compositions containing either modifier, or both modifiers incombination, allows for the accomplishment of the contour without voidsand gaps because the material offers resistance to packing. Thecondensable compositions of the present invention are also useful forthose restorations not requiring a matrix band, such as Class I, III andV.

The rheological modifiers may be added directly during the mixing of thepaste when the resin and the filler are combined in a planetary mixer.Alternatively, a solution of the rheological modifier in a volatilesolvent, such as 10 percent modifier in ethanol, may be sprayed on thefiller, followed by drying. This is the preferred method for formulatingthe rheological modifier into composites that are self-cured andpowder-liquid. The modifier is added in an amount effective to achievethe desired properties of reduced volumetric shrinkage and shrinkagestress and improved condensability. This amount is variable depending onthe compositions used for the resin and filler, but for example therange of 0.1 to 5 weight percent is contemplated. For the Formula 1modifier the amount is likely to be in the range of about 0.1 to about0.7 weight percent and about 0.1 to about 1.5 weight percent for theFormula 2 modifier. If too much modifier is added, the composite becomestoo thick and will be difficult to manufacture and manipulate. If toolittle modifier is added, the desired effects will not be achieved. In apreferred embodiment of the present invention, 0.3 to 0.6 weight percentof Formula 1 modifier or 0.5 to 1.2 weight percent of Formula 2 modifieris added to the composite paste.

When the cavity to be filled is more than 2 mm deep, conventionallight-cured resin-based composites must be layered with a layerthickness of 2 mm maximum in order to minimize the effects of theshrinkage occurring during polymerization. Because the compositions ofthe present invention show reduced shrinkage when cured and permitadequate depth of cure, the layering technique used during the placementof conventional light-cured resin-based composites can be eliminated orthe layer thickness can be significantly increased, making placementsimpler and less technique-sensitive when using the compositions of thepresent invention. The following examples will further illustrate theadvantages of this aspect of the present invention.

EXAMPLE 1

One control sample and two test samples were prepared according to thefollowing method. A methacrylate resin, as described in Table 1, wasintroduced in a planetary mixer and thermostated to 50° C. A rheologicalmodifier according to Formula 1 was then added to the resin of testsample 2 and a rheological modifier according to Formula 2 was added tothe resin of test sample 3. The mixer was started for about 5 minutes tomix the resin phase and then the filler containing the physicallyadmixed components listed in Table 2 was slowly added over a period of3-5 hours. Mixing was continued for another hour and the resultant pastewas deaerated under attenuated oxygen pressure. Table 3 details thephysical properties of the sample pastes prepared. All measurements werecarried out using standard ISO methods except where indicated, and thestandard deviations are provided in parentheses.

                  TABLE 1                                                         ______________________________________                                        Resin Composition                                                             ______________________________________                                        Ethoxylated Bisphenol A Dimethacrylate                                                                71.1 weight %                                           2-Ethylhexyl-4-(dimethylamino)benzoate  0.49 weight %                         Camphorquinone  0.17 weight %                                                 2-Hydroxy-4-methoxy Benzophenone  0.49 weight %                               (BHT) Butylated Hydroxytoluene  0.05 weight %                                 Total 100                                                                   ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Filler Composition                                                            ______________________________________                                        Barium Aluminum Borosilicate, silanated                                                                91.4 weight %                                          20 nm.sup.1 Hydrophobic fumed silica (TS-530).sup.2  4.3 weight %                                    40 nm.sup.1 Fumed Silica, silanated (OX-50).sup.3                              4.3 weight %                                          Total 100                                                                   ______________________________________                                         .sup.1 average particle size                                                  .sup.2 Degussa Corp., Ridgefield Park, N.J.                                   .sup.3 Degussa Corp., Ridgefield Park, N.J.                              

It should be appreciated that alternative monomers to those listed inTable 1 above may be utilized in the resin composition. For example,BisGMA (Bisphenol A diglycidyl ether dimethacrylate), ethoxylatedBisphenol A dimethacrylate, diethylene glycol dimethacrylate,triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate,1,6-hexanediol dimethacrylate, 1,12-dodecanediol dimethacrylate,diurethane dimethacrylate (Rohamere 6661-0, Huls America, SomersetN.J.), trimethylolpropane trimethacrylate, glyceryl dimethacrylate,neopentylglycol dimethacrylate. Similarly, with respect to the fillercomponents listed in Table 2 above, alternative filler components may beutilized for the filler composition. For example, inorganic glasses andcrystalline compounds such as: quartz cristoballite, silica, alumina,glass ceramics such as aluminosilicate glass ceramic, zirconiumsilicate, strontium aluminumborosilicate; and organic materials such assplintered pre-polymerized particles used for the preparation ofinhomogeneous microfill dental composites.

                  TABLE 3                                                         ______________________________________                                        Physical Properties of Composites                                                           Control   Test      Test                                          Sample 1 Sample 2 Sample 3                                                  ______________________________________                                        % Rheological Modifier                                                                      0         0.5.sup.1 1.0.sup.2                                     Wt. % Filler Load 77.0 77.0 77.0                                              Depth of Cure (mm) at 600 4.7 (0.1) 5.0 (0) 4.52 (0)                          mw/cm.sup.2, 4 mm diameter                                                    Rockwell Hardness (15T).sup.3 79.7 (0.6) 78.5 (0.4) 76.8 (0.8)                Compressive Strength (MPa) 379 (20) 356 (24) 273 (36)                         Flexural Strength (MPa) 137 (23) 119 (23) 120 (18)                            Flexural Modulus (MPa) 10,192 (599) 10,164 (594) 9,481 (978)                  % Volumetric Shrinkage.sup.4 3.14 (0.03) 1.76 (0.26) 1.48 (0.08)                                               Penetrometer (mm).sup.5 4.2 (0.1) 2.1                                        (0.1) 2.0 (0.1)                               Needle, 1 mm)                                                                 G' at 10 ksec (KPa) 100 4,500 7,410                                           Normal Force (g).sup.6 40 737 1,330                                         ______________________________________                                         .sup.1 BYK 405, BYK Chemie USA, Wallingford, CT                               .sup.2 Thixatrol ® VF10, Rheox Corp. Hightstown, NJ                       .sup.3 Average of 3 measurements on the surface of a cylindrical sample 1     mm in diameter and 4 mm in height. The samples were light cured for 40        seconds, and stored in water for 24 hours at 37° C. prior to           measurement.                                                                  .sup.4 Buoyancy method in water was used. The shrinkage was measured by       the difference of densities before and after cure for a 1 g diskshaped        sample. The average of 3 samples is reported.                                 .sup.5 Precision Penetrometer (GCA Corp., Chicago, IL) with a 1 mm needle     was used with no additional weight (0 g). The paste was placed in a mold      10 mm in diameter and 8 mm in height. An average of 3 measurements is         reported. Penetration was performed for 10 seconds.                           .sup.6 Elastic modulus (G') of uncured paste is measured using an SR200       stress rheometer (Rheometrics Scientific, Piscataway, NJ) in the              plateplate configuration. The plate diameter was 10 mm with a gap spacing     of 0.5 mm and the plate surfaces were sandblasted with 100 micron alumina     The measurement was made in the oscillatory mode at 0.1 rad./sec at 0.5%      strain max. at 30° C. An initial weight of approximately 2 kg is       applied on the composite in the axial direction to allow it to conform  #     to the dimensions of the gap. When the 0.5 mm gap is reached, the Normal      Force is the paste resistance in the axial direction when the paste is        allowed to relax for 10 ksec after application of the initial weight.    

The properties shown in Table 3 demonstrate that the use of therheological modifier in test samples 2 and 3 reduced volumetricshrinkage by over 50% in comparison to the composite of control sample1, which did not contain a modifier according to the present invention.By adding the theological modifier according to the principles of thepresent invention, a volumetric shrinkage of less than about 2% may beachieved. In addition, the elastic modulus (G') of the uncuredcomposites containing a rheological modifier were increasedconsiderably, resulting in increased condensability. Furthermore, thedepth of cure and other critical properties of the composites, such ashardness and flexural strength, were not negatively impacted to anyappreciable extent by the addition of the modifiers.

Dental Restorative Composite with Dispersant

Inclusion of a novel dispersant in dental composite formulations of thepresent invention results in increased filler loading and decreasedviscosity, which after curing provides a dental restorative with reducedshrinkage, a lower coefficient of thermal expansion and generallyimproved physical properties. Suitable dispersants useful in the presentinvention are phosphoric acid esters (including mono-, di- andtri-esters). Particularly, phosphoric acid esters useful in the presentinvention are selected from the following: a) a phosphoric acid estercontaining a carboxylic acid ester group and an ether group, and b) aphosphoric acid ester containing a carboxylic acid ester group and notcontaining an ether group. These dispersants are effective withnonaqueous, highly-filled suspensions containing polymerizable groups(e.g., acrylic and methacrylate esters) used for dental purposes and,more particularly, with highly-filled glass suspensions containingmethacrylate resins. The dispersants useful in the present inventionpreferably comprise 5 weight percent or less of the composite paste. Toobtain good uniformity of distribution of the dispersant in the finalcomposite paste, the dispersant is first mixed with the resin, followedby the slow addition of the filler material.

In one embodiment of the present invention, the dispersant is aphosphoric acid ester with the following structure: ##STR7## where n isequal to 5 to 10 and m is equal to 1 to 20.

The presence of the carboxylic acid ester group of the dispersant of thepresent invention results in excellent compatibility with(meth)acrylate-based resin systems. In a preferred embodiment of thepresent invention, the dispersant with the structure described byFormula 3 has a value m of 1 to 2 and a value n of 5 to 9. In a furtherpreferred embodiment, the Formula 3 dispersant is preferably about 0.5to about 3.5 weight percent of the composite paste. The followingexamples will further illustrate this aspect of the present invention.

EXAMPLE 2

Three samples (test samples 4-6) incorporating the above describedFormula 3 dispersant were prepared according to the following method. Amethacrylate resin, as described in Table 1 above, was introduced into aplanetary mixer and thermostated to 50° C. For test samples 4-6, aphosphate ester with the structure described above in Formula 3 having avalue m of 1 and a value n of 5-10 was added to the resin. Thedispersant tested was obtained from BYK Chemie USA, Wallingford, Conn.under the trade name Disperbyk®-111, which may be disclosed in U.S. Pat.No. 5,151,218, the entire disclosure of which is hereby incorporated byreference. The mixer was started for about 5 minutes to mix the resinphase and then the filler containing the physically admixed componentslisted in Table 2 above was slowly added over a period of about 3 hours.Mixing was continued for another hour and the resultant paste wasdeaerated under attenuated oxygen pressure. Table 4 details the physicalproperties of the three test sample pastes prepared along with theproperties of control sample 1. All measurements were carried out usingstandard ISO methods except where indicated, and the standard deviationsare provided in parentheses.

                  TABLE 4                                                         ______________________________________                                        Physical Properties of Composites                                                          Control  Test     Test   Test                                      Sample Sample Sample Sample                                                   1 4 5 6                                                                     ______________________________________                                        Formula 3    0.0      0.8      1.5    3.0                                       Dispersant Wt. %                                                              Wt. % Filler Load 77 (57.5) 78.5 80 (61.7) 82 (64.9)                          (Vol. % Load)                                                                 Depth of Cure at 4.7 (0.1) 4.96 (0.1) 4.5 (0.1) 4.65 (0.1)                    600 mw/cm.sup.2, 4 mm                                                         diameter                                                                      Rockwell Hardness 79.7 (0.6) 81.0 (1.1) 82.2 (0.3) 78.7 (0.7)                 (15T).sup.2                                                                   Compressive 379 (20) 320 (23) 343 (25) 325 (15)                               Strength (MPa)                                                                Flexural Strength 137 (23) 130 (16) 118 (12) 104 (9)                          (Mpa)                                                                         Flexural Modulus 10,192 10,918 10,175 9,272                                   (MPa) (599) (433) (468) (509)                                                 % Volumetric 3.14  2.92 2.44 2.11                                             Shrinkage.sup.3 (0.03) (0.07) (0.25) (0.06)                                   Penetrometer (mm).sup.4 4.2 (0.1) 3.2 (0.1) 2.3 (0.1) 2.9 (0.2)                                                    0 g, (Needle, 1 mm)                      Penetrometer (mm).sup.5 2.8 (0.2) 1.5 (0.1) 1.6 (0.1) 1.2 (0.1)                                                    0 g, (Flathead, 1 mm)                  ______________________________________                                         .sup.1 Disperbyk 111, BYK Chemie USA, Wallingford, CT                         .sup.2 Average of 3 measurements on the surface of a cylindrical sample 1     mm in diameter and 4 mm in height. The samples were light cured for 40        seconds, and stored in water for 24 hours at 37° C. prior to           measurement.                                                                  .sup.3 Buoyancy method in water was used. The shrinkage was measured by       the difference of densities before and after cure for a 1 g diskshaped        sample. The average of 3 samples is reported.                                 .sup.4 Precision Penetrometer (GCA Corp., Chicago, IL) with a 1 mm needle     was used with no additional weight (0 g). The paste was placed in a mold      10 mm in diameter and 8 mm in height. An average of 3 measurements is         reported. Penetration was performed for 10 seconds.                           .sup.5 Same test as above, but using a flat head rather than a needle, to     simulate the effect of the impact from dental instruments having a flat       head on the composite.                                                   

A comparison of control sample 1 with test sample 5 demonstrates thatthe volume filler load may be increased from 57.5% to 61.7% (from 77 to80 wt. %) by the addition of the phosphate ester while the viscosityremains similar to the viscosity of the control sample. The penetrometerreading is a measure of viscosity to a certain extent, but no directrelationship has been established. The G' and Normal Force measurements,as reported in Table 3, although useful for composite pastes containingthe rheological modifier, have proven unreliable when a dispersant isadded to the paste. Table 4 further shows that the physical propertiesof the composite pastes were not negatively impacted by the addition ofthe dispersant. Further increase of volume load to 64.9% (82 wt. %) asshown in test sample 6, although resulting in a decrease in flexuralstrength, provides physical properties that still satisfy the AmericanDental Association guidelines for restorative composites. The tests alsodemonstrate that a reduction of volumetric shrinkage of about 30% may beachieved by the volume load increase from 57.5% to 61.7%, as shown intest sample 5. This is expected to result in improved adaptation whenplaced in a tooth cavity and cured.

In another embodiment of the present invention, the dispersant is aphosphoric acid ester with the following structure: ##STR8## where R isa (meth)acrylate group radical.

Again, the presence of the carboxylic acid ester group of the abovedispersant (Formula 4) results in excellent compatibility with(meth)acrylate-based resin systems. In a preferred embodiment, the abovedispersant of the present invention having the structure shown inFormula 4, R is one of the following: ##STR9##

Each of Compounds 1-5 may be prepared in two steps. In the first step,the hydroxy functional methacrylate is condensed with caprolactone underring-opening polymerization conditions in the presence of catalyticamounts of SnCl₂ to prepare a polyester. In the second step, thepolyester is reacted with polyphosphoric acid (117.5% concentration) at65° C. to give the phosphoric acid ester. By way of example, thereaction sequence is shown below for the preparation of the hydroxyethylmethacrylate (HEMA) derivative Compound 1: ##STR10## In a furtherpreferred embodiment of the present invention, the Formula 4 dispersantis preferably added at about 0.5 to about 3.5 weight percent of thecomposite paste. The following examples will further illustrate thisaspect of the present invention.

EXAMPLE 3

In a 4-neck reaction kettle containing an air flow tube, a thermocouple,a condenser and a stirrer, 26.0 parts by weight of hydroxyethylmethacrylate (HEMA) were combined with 114.1 parts by weight ofcaprolactone, 0.14 parts by weight of methyl ether of hydroquinone(MEHQ) and 0.007 parts by weight of stannous chloride under a flow ofdry air. The mixture was thermostated at 120° C. and stirring wascontinued for 18 hours. The disappearance of the caprolactone wasmonitored with HPLC (High Pressure Liquid Chromatography) using areverse phase column with 70/30 acetonitrile/water as eluant. Theresultant liquid polycaprolactone-modified HEMA was essentiallycolorless.

In a three neck flask equipped with a stirrer and a condenser under aconstant flow of dry air, 70.0 grams of the above product(polycaprolactone-modified HEMA) was combined with 8.45 grams of 117.5%phosphoric acid. The mixture was heated with stirring for 4 hours at 70°C. A light yellow oil resulted. Titration with 0.1N NaOH showed that thephosphoric acid ester was formed.

Various Formula 4 methacrylate derivatives prepared using the aboveprocedures are listed in Table 5.

                  TABLE 5                                                         ______________________________________                                        Polycaprolactone-Modified Methacrylate Monophosphates                                                     Caprolactone:                                                                           Molecular                                   starting material Weight                                                    Compound Starting Material (mole ratio) Average                             ______________________________________                                        1a      Hydroxyethyl Methacrylate                                                                     1:1         324                                          (HEMA)                                                                       1b HEMA 2:1 438                                                               1c HEMA 5:1 780                                                               1d HEMA 7:1                                                                   2 Hydroxyethyl acrylate 5:1 766                                                (HEA)                                                                        3 Polypropylene 5:1 713                                                        glycomethacrylate                                                             (PPGMA)                                                                      4a Glycerol Dimethacrylate 2:1 536                                             (GDMA)                                                                       4b GDMA 5:1 879                                                               5a Dipentaerythritol 2:1 713                                                   pentaacrylate (DPEPA)                                                        5b DPEPA 5:1 1175                                                           ______________________________________                                    

All of the above compounds may be used as dispersants in highly filledglass suspensions containing methacrylate resins. Nine test samples(test samples 7-15) were prepared according the following method. Amethacrylate resin, as described in Table 1 above, was introduced into aplanetary mixer and thermostated to 50° C. The phosphate ester with thestructure described above by Formula 4 was then added to the resin so asto comprise 1.5 weight percent of the total resin/filler mixture with an80 weight percent filler loading. The mixer was started for a fewminutes to mix the resin phase and then the filler containing thephysically admixed components listed in Table 2 above was slowly addedover a period of about 3 hours. Mixing was continued for another hourand the resultant paste was deaerated under attenuated oxygen pressure.Table 6 details the physical properties of the Formula 4 test samplepastes (7-15) prepared along with the properties of control sample 1 andtest sample 5 (containing a Formula 3 dispersant). All measurements werecarried out using standard ISO methods except where indicated, and thestandard deviations are provided in parentheses.

                                      TABLE 6                                     __________________________________________________________________________    Physical Properties of Pastes Prepared with Various Dispersants               __________________________________________________________________________                      Control                                                                            Test  Test Test Test   Test                               Sample 1 Sample 5 Sample 7 Sample 8 Sample 9 Sample 10                     __________________________________________________________________________      Dispersant, 1.5 Wt. % None Disperbyk ® 1b 1c 1d 2                         Wt % Filler Load (Vol. % Load) 77 80 80 80 80 80                              Depth of Cure at 600 mw/cm.sup.2, 4 mm 4.7 4.5 4.2 4.6 4.0 4.2                diameter (0.1) (0.1) (0.1) (0.1) (0.1) (0.1)                                  Rockwell Hardness (15T).sup.1 79.7 82.2 84.4 83.4 82.4 83.3                    (0.6) (0.3)  (0.38) (0.1) (0.3) (0.3)                                        Compressive Strength (MPa) 379 343 290 399 375 314                             (20)   (25)   (62)   (21)   (17)   (29)                                      Flexural Strength (MPa) 137 118 124 129 120 127                                (23)   (12)   (22)   (12)   (9)   (14)                                       Flexural Modulus (MPa) 10,192 10,175 11,362 11,189 10,827 12,187                                                            (599)    (468)    (773)                                                      (968)    (1,035)                                                             (1,754)                           Penetrometer (mm).sup.2 0 g, (Needle, 1 mm) 4.2 2.3 3.6 >8.0 >8.0 >8.0                                                      (0.1) (0.1) (0.1)                                                            Penetrometer (mm).sup.3 0                                                    g, (Flathead, 1 mm) 2.8 1.6                                                   .3 >8.0 >8.0 7.1                   (0.2) (0.1) (0.2)   (0.1)                                                    Penetrometer (mm).sup.3 0 g, (Flathead, 2 mm)    5.7 4.5                          (0.1) (0.1)                                                             __________________________________________________________________________                          Test   Test Test   Test   Test                             Sample 11 Sample 12 Sample 13 Sample 14 Sample 15                          __________________________________________________________________________      Dispersant, 1.5 Wt. % 3 4a 4b 5a 5b                                           Wt % Filler Load (Vol. % Load) 80 80 80 80 80                                 Depth of Cure at 600 mw/cm.sup.2, 4 mm 3.9 4.4 4.1 4.1 4.5                    diameter  (0.03) (0.1) (0.3) (0.1) (0.2)                                      Rockwell Hardness (15T).sup.1 83.1 84.0 83.9 83.6 83.3                         (0.3) (0.5) (0.1) (0.4) (0.1)                                                Compressive Strength (MPa) 341 394 408 387 381                                 (29)   (43)   (34)   (27)   (27)                                             Flexural Strength (MPa) 110 114 125 105 106                                    (11)   (22)   (26)   (12)   (6)                                              Flexural Modulus (MPa) 11,460 11,977 10,571 12,404 11,664                      (1,045)     (899)    (2,051)     (1,006)     (619)                           Penetrometer (mm).sup.2 0 g, (Needle, 1 mm) 5.5 2.1 6.2 2.7 3.0                                                               (0.1) (0.2) (0.2) (0.2)                                                     0.1)                            Penetrometer (mm).sup.3 0 g, (Flathead, 1 mm) 2.3 1.3 4.3 1.5 1.0                                                             (0.1) (0.1) (0.1) (0.1)                                                     0.1)                            Penetrometer (mm).sup.3 0 g, (Flathead, 2 mm)                               __________________________________________________________________________     .sup.1 Average of 3 measurements on the surface of a cylindrical sample 1     mm in diameter and 4 mm in height. The samples were light cured for 40        seconds, and stored in water for 24 hours at 37° C. prior to           measurement.                                                                  .sup.2 Precision Penetrometer (GCA Corp., Chicago, IL) with a 1 mm needle     was used with no additional weight (0 g). The paste was placed in a mold      10 mm in diameter and 8 mm in height. An average of 3 measurements is         reported. Penetration was performed for 10 seconds.                           .sup.3 Same test as above, but using a flat head rather than a needle, to     simulate the effect of the impact from dental instruments having a flat       head on the composite.                                                   

The properties shown in Table 6 demonstrate that there is a dramaticreduction of viscosity of the pastes where the phosphate esters ofCompound 1 are included. As stated previously, the penetrometer test isindicative of the viscosity of the paste, although not directly related.There is also demonstrated a substantial increase of the dispersanteffect (decrease in viscosity) of the Formula 4 dispersants whencompared with the commercial material Disperbyk®-111 (Formula 3dispersant). Furthermore, the physical properties of the composites arenot significantly reduced by the addition of thepolycaprolactone-modified methacrylate monophosphates.

As a further comparison, the most efficient dispersant listed above,Compound 1c, was also formulated in pastes at different loads andamounts (test samples 16-18). The results of test samples 8 and 16-18are listed in Table 7.

                  TABLE 7                                                         ______________________________________                                        Compound 1c at Various Loadings                                                         Test      Test     Test    Test                                       Sample Sample Sample Sample                                                   8 16 17 18                                                                  ______________________________________                                        Wt. % Compound                                                                          1.5       1.5      2.0     3.0                                        1c dispersant                                                                 Wt. % Filler Load 80 76 82 82                                                 Penetrometer >8.0 --  4.4(0.2) >8.0                                           (mm) 0 g, (Flat-                                                              head, 1 mm)                                                                   Penetrometer 6.6 (0.0) 4.6 (0.2) 2.0 (0.2) 5.1 (0.0)                          (mm) 0 g, (Flat-                                                              head, 2 mm)                                                                   Depth of Cure at 4.6 (0.1) 4.8 (0.1) 4.5 (0.1) 4.2 (0.1)                      600 mw/cm2,                                                                   4 mm diameter                                                                 % Volumetric 2.60 (0.18) 2.91 2.37 (0.08) 2.50 (0.25)                         Shrinkage  (0.4)                                                              Rockwell 83.4 (0.1) 80.9 84.7 (0.4) 82.2 (0.2)                                Hardness 15T  (0.5)                                                           Compressive 399 (21) 350 (28) 312 (48) 274 (25)                               Strength (MPa)                                                                Flexural Strength 129 (12) 139 (13) 132(17) 105 (14)                          (MPa)                                                                         Flexural Modulus 11,189 12,297 12,159 10,471                                  (MPa) (968) (727) (1,038) (741)                                             ______________________________________                                    

The results shown in Table 7 demonstrate that a low relative viscositypaste having acceptable physical properties may be prepared at 82%filler loading with only 2% Formula 4 dispersant based on a 1c Compound.In contrast, pastes incorporating no dispersant cannot be made with afiller loading above 5 77%. See Control Sample 1 in Table 6.

Dental Restorative Composite with Fluorocopolymer

In a further aspect of the present invention, an effective amount of aknown fluorocopolymer material such as that disclosed in Yamabe et al.U.S. Pat. No. 4,345,057, the entire disclosure of which is incorporatedherein by reference, is added to the resin/filler mixture to provide adental restorative composite of the present invention that possessesimproved wear properties when used in the mouth. The material describedin the Yamabe et al. patent and to be used as an additive for the dentalrestorative of the present invention is a fluorocopolymer of afluoroolefin, a cyclohexyl vinyl ether, an alkyl vinyl ether and ahydroxyalkyl vinyl ether. For use in the present invention, thefluorocopolymer additive comprises the above four components at ratiosof about 40-60 mole % fluoroolefin units, about 5-45 mole % cyclohexylvinyl ether units, about 5-45 mole % alkyl vinyl ether units and about3-15 mole % hydroxyalkyl vinyl ether units. Preferably, thefluorocopolymer additive comprises the above four components at ratiosof about 45-55 mole % fluoroolefin units, about 10-30 mole % cyclohexylvinyl ether units, about 10-35 mole % alkyl vinyl ether units and about5-13 mole % hydroxyalkyl vinyl ether units. In a preferred embodiment ofthe present invention, the fluorocopolymer comprises about 10 weightpercent or less of the composite paste, and more preferably, less than 1weight percent.

The fluorocopolymer used in the present invention is soluble in(meth)acrylate resins, in particular dimethacrylate resins, does notinterfere in a deleterious manner with the curing of the paste and doesnot negatively influence the physical and aesthetic properties of theresultant composite after curing. The following examples will furtherillustrate this aspect of the present invention.

EXAMPLE 4

Four samples (test samples 19-22) incorporating a fluorocopolymer intothe composite resin of the present invention were prepared according tothe following method. A methacrylate resin, as described in Table 1above, was introduced in a planetary mixer and thermostated to 50° C. Afluorocopolymer LF-200 (supplied by Zeneca Resins Co., Wilmington,Mass.) was added to the resin. A suitable alternative fluorocopolymer isX-910LM (also available from Zeneca Resins). Initially, thefluorocopolymer is supplied as a 60% solution in xylene, but the xyleneis evaporated in a vacuum at 80° C. and 0.1 Torr. The resin mix used intest samples 19-22 contained the evaporated fluorocopolymer in an amountof 3.6 wt. % and the resin of Table 1 in an amount of 96.4 wt. %. Themixer was started for about five minutes to mix the resin phase and thenthe filler containing the physically admixed components listed in Table2 above was slowly added over a period of 3-5 hours to a filler loadingof 77 wt. %. Mixing was continued for another hour and the resultantpaste was deaerated under attenuated oxygen pressure. Table 8 detailsthe physical properties of the test sample pastes 19-22 prepared alongwith the properties of control sample 1. All measurements were carriedout using standard ISO methods except where indicated, and the standarddeviations are provided in parentheses.

                  TABLE 8                                                         ______________________________________                                        Physical Properties of Composites                                                     Control  Test     Test   Test   Test                                    Sample Sample Sample Sample Sample                                            1 19 20 21 22                                                               ______________________________________                                        Wt. %   0        0.28     0.55   0.83   1.00                                    Flouroco-                                                                     polymer.sup.1                                                                 Wt. % Filler 77.0 77.0 77.0 77.0 77.0                                         Load                                                                          Depth of 4.7 4.49 4.12 4.26 4.60                                              Cure (0.1) (0.02) (0.01) (0.20) (0.0)                                         (mm).sup.2 at                                                                 600 mw/cm.sup.2                                                               (4 mm                                                                         diameter)                                                                     Translucency 25.2 25.6 23.6 23.4 22.1                                         (1 mm)                                                                        Rockwell 79.7 82.4 82.0 82.6 81.2                                             Hardness (0.6) (0.13) (0.1) (0.3) (0.5)                                       (15T).sup.2                                                                   Compressive 379 (20) 383 (35) 392 (27) 384 (37) 311 (25)                      Strength                                                                      (MPa)                                                                         Flexural 137 (23) 132 (17) 139 (16) 126 (9) 121 (12)                          Strength                                                                      (MPa)                                                                         Flexural 10,192 10,828 10,800 10,800 11,070                                   Modulus (599) (954) (950) (900) (541)                                         (MPa)                                                                         Penetrometer 4.2 (0.1) 3.7 (0.2) 5.7 (0.2) 4.0 (0.3) 3.3 (0.2)                (mm).sup.4, 0 g                                                               (Needle,                                                                      1 mm)                                                                         Penetrometer 2.8 (0.2) 3.3 (0.3) 1.6 (0.1) 1.5 (0.3) 1.2 (0.1)                (mm).sup.3, 0 g                                                               (Flathead,                                                                    1 mm)                                                                         3 Body Wear 9.1 × 10.sup.-9  1.2 × 10.sup.-8 3.5 ×                                                10.sup.-9 3.95 × 10.sup.-9                                               Rate                                   (cc/cycle).sup.4                                                              Number of 2.0 × 10.sup.5  1.2 × 10.sup.5 3.0 ×                                                    10.sup.5 1.8 × 10.sup.5                                                  Cycles Run                           ______________________________________                                         .sup.1 Lumiflon LF200, Zeneca Resins, Wilmington, MA                          .sup.2 Average of 3 measurements on the surface of a cylindrical sample 1     mm in diameter and 4 mm in height. The samples were light cured for 40        seconds, and stored in water for 24 hours at 37° 0 C. prior to         measurement.                                                                  .sup.3 Precision Penetrometer (GCA Corp., Chicago, IL) with a 1 mm needle     or a 1 mm flathead was used with no additional weight (0 g). The paste wa     placed in a mold 10 mm in diameter and 8 mm in height. An average of 3        measurements is reported. Penetration was performed for 10 seconds.           .sup.4 The wear test was performed in the 3body wear mode using               specialized apparatus. A disk of the cured composite, 26 mm in diameter       and 1.0 mm thick, was abraded against the flat end of a 13 mm in diameter     glass ceramic rod (Macor, Dow Corning Corp., Corning, NY) having              equivalent hardness to enamel inside a cup. The cup was charged with 10 g     polyethyl methacrylate beads (Ionac 26F, Sybron Chemicals Corp.,              Birmingham, NJ) suspended in water at a ratio of 1:1 to simulate the food     bolus. The compo  #site disk was rotated at about 2 Hz while the rod came     in contact with the disk surface in an up and down motion of 0.33 Hz usin     a vertically positioned cam shaft. The maximum contact pressure was 35        MPa. The bead slurry was changed every 10 kcycles and the weight of the       disk was measured every 30 kcycles.                                      

The properties shown in Table 8 demonstrate that the addition of asoluble fluorocopolymer at a total concentration of less than 1 weightpercent of the resin/filler mixture reduces the wear of the composite,in particular reduces the wear rate in a three body wear test to lessthan half the value for the composite without the addition. Furthermore,the physical and aesthetic properties of the composite are notsignificantly effected. Namely, the translucency, depth of cure andflexural strength and modulus of the resulting composite remained aboutthe same as that of the composite not containing the fluorocopolymeradditive (Control Sample 1).

Dental Restorative Composite with Rheological Modifier, Dispersant andFluorocopolymer Additive

The addition of a combination of the described additives provides adental restorative composite with superior properties to that of acomposite with no such additives. Eight test samples were preparedaccording to the above described methods. Test samples 23 and 24 combinethe resin/filler mixture with a Formula 1 rheological modifier andFormula 3 dispersant. Test samples 25-27 combine the resin/fillermixture with varying amounts of a Formula 1 rheological modifier andvarying amounts of a Formula 4 dispersant based on Compound 1c. Testsamples 28-30 also add a fluorocopolymer to one of the abovecombinations. Table 9 details the physical properties of the samplepastes prepared.

                                      TABLE 9                                     __________________________________________________________________________    Properties of Pastes with a Combination of Additives                                     Control                                                                            Test Test  Test Test  Test  Test  Test  Test                    Sample 1 Sample 23 Sample 24 Sample 25 Sample 26 Sample 27 Sample 28                                                                Sample 29 Sample                                                              30                    __________________________________________________________________________    Wt. % Formula 1                                                                          0    0.5  0.45  0.3  0.3   0.5   0.5   0.3   0.2                     Rheological Modifier                                                          Wt. % Formula 3 Disper- 0 2.0 1.45 0 0 0 0 0 2.0                              sant                                                                          Wt. % Formula 4 Disper- 0 0 0 3.00 1.50 2.0 2.0 2.0 0                         sant of Compound 1c                                                           Wt. % Fluorocopolymer 0 0 0 0 0 0 0.40 0.72 0.72                              Wt. % Filler Load 77 80 80 82 80 80 80 80 80                                  Depth of Cure (mm) at 4.7 4.2 4.68 4.29 4.1 4.1 3.8 4.1 3.8                   600 mw/cm.sup.2 (4 mm (0.1) (0.1) (0.04)  (0.10) (0.1) (0.0) (0.1)                                                                  (0.0) (0.1)                                                                    diameter)                                                                     Rockwell                                                                     Hardness (15T)                                                                79.7 81.3 80.7                                                                83.1 83.2 83.2                                                                81.9 81.6 81.0                                                                  (0.6)  (0.19)                                                               (0.3) (0.2)                                                                   (0.13)  (0.16)                                                                (0.3) (0.5)                                                                    Compressive                                                                  Strength 379 302                                                              317 285 343 285                                                               310 338 297                                                                    (MPa) (20)                                                                   (21)   (27)                                                                   (34)   (33)                                                                   (16)   (22)                                                                   (18)   (26)                                                                    Flexural                                                                     Strength (MPa)                                                                137 98 120 121                                                                110 108 117 122                                                               117                      (23)   (11)   (11)    (14)   (15)   (9)   (9)   (4)   (15)                   Flexural Modulus (MPa) 10,192 9,979 9,660 11,080 11,693 10,763 10,599                                                               11,392 9,763                                                                    (599)    (644)                                                                (708)    (619)                                                                (664)    (898)                                                                (480)    (639)                                                                (1,170)                                                                      % Volumetric                                                                 Shrinkage 3.14                                                                1.54 1.75 1.58                                                                1.53 0.86 1.74                                                                1.77                      (0.03)  (0.17) (0.04)  (0.48)  (0.26)  (0.33)  (0.16) (0)                   G' at 10 ksec (KPa) 100 4,800 1,440 1,440 3,390 3,880 1,710                   Normal Force (g) 40 700 565 850 1,315 1,306 1,150                             Penetrometer (mm), 150 >8.0 4.7 5.1 4.8 7.4 4.45 3.4 4.5 5.0                  g (Needle, 1 mm) (0.1) (0.1) (0.2)  (0.2) (0.2) (0.1) (0.1) (0.1)                                                                    3 Body Wear Rate                                                             (cc/ 9.1 ×                                                              10.sup.-9    1.05                                                             × 10.sup.-8                                                             4.09 ×                                                                  10.sup.-9 1.10                                                                × 10.sup.-9                                                             4.50 ×                                                                  10.sup.-9 4.09                                                                × 10.sup.-9       cycle).sup.5                                                                  Number of Cycles Run 2.0 × 10.sup.5      2.0 × 10.sup.5 3.0                                                             × 10.sup.5                                                              2.42 ×                                                                  10.sup.5   3.0                                                                × 10.sup.5                                                              3.0 ×                                                                   10.sup.5              __________________________________________________________________________

The various compositions were tested to determine the amount of eachadditive required to optimize condensability, shrinkage, wear andphysical properties. It was found that there is substantial interplaybetween the rheological modifier and the fluorocopolymer, because bothadditives affect the thixotropic properties of the composite. Forexample, the theological modifier thickens and renders the compositepaste thixotropic, while the dispersant makes the paste thinner andallows for higher loading. The blending of the effects of therheological modifier and the dispersant provides a composite materialwith improved handling. While in the abstract these different additivesappear to have a contradictory effect, the sum total effect is asuperior dental composite material with improved handling. Thus,overall, the various properties of a composite paste are optimized whenall three additives are combined within the resin/filler mixture. Asshown in Table 9, test samples 27 and 28 provided the best overallproperties with the additives present in the noted amounts.

In one of its most preferred forms, the dental composite of the presentinvention is comprised of about 80 wt. % filler as described in Table 2,about 0.2 to about 0.3 wt. % of a Formula 1 rheological modifier, about2 wt. % of a Formula 3 dispersant or a Formula 4 dispersant based onCompound 1c, about 0.72 wt. % of a fluorocopolymer, and the balancebeing the resin as described in Table 1. This formulation is believed tohave a layer depth limit of about 4 mm. Where greater layer depths aredesired, up to 5 mm or more, it is advantageous to utilize a formulationthat does not include the fluorocopolymer component, althoughsacrificing the improved wear resistance that the fluorocopolymerprovides. In all other respects, the above preferred formulation wouldremain the same.

While the present invention has been illustrated by the description ofan embodiment thereof, and while the embodiment has been described inconsiderable detail, it is not intended to restrict or in any way limitthe scope of the appended claims to such detail. Additional advantagesand modifications will readily appear to those skilled in the art. Forexample, the quantity of the rheological modifier, dispersant and/orfluorocopolymer to be added to the resin/filler mixture will vary basedon the particular compositions used for the resin and the filler. Theinvention in its broader aspects is therefore not limited to thespecific details, representative method and illustrative examples shownand described. Accordingly, departures may be made from such detailswithout departing from the scope or spirit of applicant's generalinventive concept.

What is claimed is:
 1. A dental restorative comprised of:a filler; apolymerizable acrylic monomer; and an alkylamide-containing rheologicalmodifier in an amount effective to reduce the volumetric shrinkage ofthe dental restorative during polymerization thereof.
 2. The restorativeof claim 1, wherein the amount of rheological modifier is effective toreduce the volumetric shrinkage of the dental restorative by at least50% relative to the same composition without the rheological modifier.3. The restorative of claim 1, wherein the volumetric shrinkage of thedental restorative during polymerization thereof is less than 2% asmeasured by the water buoyancy method.
 4. The restorative of claim 1,wherein the amount of rheological modifier is effective to increase thecondensability of the dental restorative relative to the samecomposition without the rheological modifier.
 5. The restorative ofclaim 1, wherein the rheological modifier is present in the range ofabout 0.1 to about 1.5 weight percent.
 6. A dental restorative comprisedof:a filler; a polymerizable acrylic monomer; and a rheological modifierin an amount effective to reduce the volumetric shrinkage of the dentalrestorative during polymerization thereof, the rheological modifierselected from the group consisting of:(1) a hydroxyfunctionalpolycarboxylic acid amide according to the formula ##STR11## wherein thesymbols have the following meanings: R=aliphatic hydrocarbon groupshaving 6 to 60 carbon atoms, or aromatic hydrocarbon groups having 6 to20 carbon atoms, or aliphatic or aliphatic/aromatic hydrocarbon radicalshaving 6 to 150 carbon atoms which are interrupted by 2, 4, 6 or 8carboxamide groups, or aliphatic hydrocarbon radicals having 4 to 150carbon atoms which are interrupted by 2 to 75 --O-- (oxygen) groups;R'=H, or C₁ to C₄ alkyl, or --Z'--(Q)_(y) --(OH)_(x) ; x=1 to 3; y=0 or1; Z=an alkylene radical having 2 to 6 carbon atoms; Z'=an alkyleneradical which is identical to or different from Z, having 2 to 6 carbonatoms; Q=an aliphatic hydrocarbon radical having 2 to 200 carbon atoms,which is linked via --O-- or ##STR12## to Z or Z' and is interrupted byzero to 99 oxygen atoms and/or carboxylic acid ester groups; and n=2 to3; and(2) the reaction product of:(a) from about 15 to 75 parts byweight of one or more liquid polyalkoxylated nitrogen-containingcompounds containing more than one hydroxyl group and which also containa pendant aliphatic radical of 6 to 40 carbon atoms selected from thegroup consisting of tertiary amines and amides of secondary amines; (b)from about 8 to 90 parts by weight of one or more polycarboxylic acids;and (c) from about 0.5 to 20 parts by weight of one or more liquiddiamines of a weight average molecular weight of about 2000 orless,wherein the reaction is continued until the acid value is withinthe range of 5 to 14 and the amine value is within the range of 42 to84.
 7. The restorative of claim 6, wherein the amount of rheologicalmodifier is effective to reduce the volumetric shrinkage of the dentalrestorative by at least 50% relative to the same composition without therheological modifier.
 8. The restorative of claim 6, wherein thevolumetric shrinkage of the dental restorative during polymerizationthereof is less than 2% as measured by the water buoyancy method.
 9. Therestorative of claim 6, wherein the amount of rheological modifier iseffective to increase the condensability of the dental restorativerelative to the same composition without the rheological modifier. 10.The restorative of claim 6, wherein the rheological modifier is presentin the range of about 0.1 to about 1.5 weight percent.
 11. Therestorative of claim 6, wherein said rheological modifier is ahydroxyfunctional polycarboxylic acid amide according to the formula##STR13## wherein the symbols have the following meanings: R=aliphatichydrocarbon groups having 6 to 60 carbon atoms, or aromatic hydrocarbongroups having 6 to 20 carbon atoms, or aliphatic or aliphatic/aromatichydrocarbon radicals having 6 to 150 carbon atoms which are interruptedby 2, 4, 6 or 8 carboxamide groups, or aliphatic hydrocarbon radicalshaving 4 to 150 carbon atoms which are interrupted by 2 to 75 --O--(oxygen) groups;R'=H, or C₁ to C₄ alkyl, or --Z'--(Q)_(y) --(OH)_(x) ;x=1 to 3; y=0 or 1; Z=an alkylene radical having 2 to 6 carbon atoms;Z'=an alkylene radical which is identical to or different from Z, having2 to 6 carbon atoms; Q=an aliphatic hydrocarbon radical having 2 to 200carbon atoms, which is linked via --O-- or ##STR14## to Z or Z' and isinterrupted by zero to 99 oxygen atoms and/or carboxylic acid estergroups; and n=2 to 3,said rheological modifier present in the range ofabout 0.1 to about 0.7 weight percent.
 12. The restorative of claim 6,wherein said rheological modifier is the reaction product of:(a) fromabout 15 to 75 parts by weight of one or more liquid polyalkoxylatednitrogen-containing compounds containing more than one hydroxyl groupand which also contain a pendant aliphatic radical of 6 to 40 carbonatoms selected from the group consisting of tertiary amines and amidesof secondary amines; (b) from about 8 to 90 parts by weight of one ormore polycarboxylic acids; and (c) from about 0.5 to 20 parts by weightof one or more liquid diamines of a weight average molecular weight ofabout 2000 or less,wherein the reaction is continued until the acidvalue is within the range of 5 to 14 and the amine value is within therange of 42 to 84, said rheological modifier present in the range ofabout 0.1 to about 1.5 weight percent.
 13. A dental restorativecomposition comprised of:a filler; a polymerizable acrylic monomer; anda phosphoric acid ester dispersant, wherein the dispersant is apolycaprolactone-modified methacrylate monophosphate.
 14. The dentalrestorative composition of claim 13, wherein the phosphoric acid esterdispersant includes a carboxylic acid ester group and an ether group.15. The dental restorative composition of claim 13, wherein thephosphoric acid ester dispersant includes a carboxylic acid ester groupand does not include an ether group.
 16. The dental restorativecomposition of claim 13, wherein the phosphoric acid ester dispersantcomprises about 5 weight percent or less of the dental restorativecomposition.
 17. A dental restorative comprised of:a filler; apolymerizable acrylic monomer; and a dispersant selected from the groupconsisting of:(1) a phosphoric acid ester according to the formula##STR15## wherein n=5 to 10 and m=1 to 20; and (2) a phosphoric acidester according to the formula ##STR16## wherein R is a (meth)acrylategroup radical.
 18. The dental restorative composition of claim 17,wherein R is a radical selected from the group consisting of: oxyethylmethacryloyl-, oxyethyl acryloyl-, polyoxypropyl methacryloyl-, glyceryldimethacryloyl-, and dipentaerythritol pentaacryloyl-.
 19. The dentalrestorative composition of claim 17, wherein the dispersant comprisesabout 5 weight percent or less of the dental restorative composition.20. The dental restorative claim 17, wherein the dispersant is aphosphoric acid ester according to the formula ##STR17## wherein n=5 to10 and m=1 to 20, said dispersant present in the range of about 0.5 toabout 3.5 weight percent of the dental restorative.
 21. The dentalrestorative of claim 17, wherein the dispersant is a phosphoric acidester according to the formula ##STR18## wherein R is a radical selectedfrom the group consisting of: oxyethyl methacryloyl-, oxyethylacryloyl-, polyoxypropyl methacryloyl-, glyceryl dimethacryloyl-, anddipentaerythritol pentaacryloyl-, said dispersant present in the rangeof about 0.5 to about 3.5 weight percent of the dental restorative. 22.The dental restorative of claim 17, wherein the dispersant is apolycaprolactone-modified methacrylate monophosphate present in therange of about 0.5 to about 3.5 weight percent of the dentalrestorative.
 23. A dental restorative composition comprised of:a filler;a polymerizable acrylic monomer; and two or more additives selected fromthe group of additives consisting of: a) an alkylamide-containingrheological modifier in an amount effective to reduce the volumetricshrinkage of the dental restorative during polymerization thereof; b) aphosphoric acid ester dispersant, wherein the dispersant is apolycaprolactone-modified methacrylate monophosphate; and c) afluorocopolymer that is soluble in a methacrylate resin.
 24. The dentalrestorative composition of claim 23, wherein the rheological modifier isselected from the group consisting of:(1) a hydroxyfunctionalpolycarboxylic acid amide according to the formula ##STR19## wherein thesymbols have the following meanings: R=aliphatic hydrocarbon groupshaving 6 to 60 carbon atoms, or aromatic hydrocarbon groups having 6 to20 carbon atoms, or aliphatic or aliphatic/aromatic hydrocarbon radicalshaving 6 to 150 carbon atoms which are interrupted by 2, 4, 6 or 8carboxamide groups, or aliphatic hydrocarbon radicals having 4 to 150carbon atoms which are interrupted by 2 to 75 --O-- (oxygen) groups;R'=H, or C₁ to C₄ alkyl, or --Z'--(Q)_(y) --(OH)_(x) ; x=1 to 3; y=0 or1; Z=an alkylene radical having 2 to 6 carbon atoms; Z'=an alkyleneradical which is identical to or different from Z, having 2 to 6 carbonatoms; Q=an aliphatic hydrocarbon radical having 2 to 200 carbon atoms,which is linked via --O-- or ##STR20## to Z or Z' and is interrupted byzero to 99 oxygen atoms and/or carboxylic acid ester groups; and n=2 to3; and(2) the reaction product of:(a) from about 15 to 75 parts byweight of one or more liquid polyalkoxylated nitrogen-containingcompounds containing more than one hydroxyl group and which also containa pendant aliphatic radical of 6 to 40 carbon atoms selected from thegroup consisting of tertiary amines and amides of secondary amines; (b)from about 8 to 90 parts by weight of one or more polycarboxylic acids;and (c) from about 0.5 to 20 parts by weight of one or more liquiddiamines of a weight average molecular weight of about 2000 orless,wherein the reaction is continued until the acid value is withinthe range of 5 to 14 and the amine value is within the range of 42 to84.
 25. The dental restorative composition of claim 23, wherein thedispersant is selected from the group consisting of:(1) a phosphoricacid ester according to the formula ##STR21## wherein n=5 to 10 and m=1to 20; and (2) a phosphoric acid ester according to the formula##STR22## wherein R is a radical selected from the group consisting of:oxyethyl methacryloyl-, oxyethyl acryloyl-, polyoxypropyl methacryloyl-,glyceryl dimethacryloyl-, and dipentaerythritol pentaacryloyl-.
 26. Thedental restorative composition of claim 23, wherein the fluorocopolymeris comprised of about 40-60 mole percent fluoroolefin units, about 5-45mole percent cyclohexyl vinyl ether units, about 5-45 mole percent alkylvinyl ether units and about 3-15 mole percent hydroxyalkyl vinyl etherunits.
 27. A dental restorative composition comprised of:a filler; apolymerizable acrylic monomer; an alkylamide-containing rheologicalmodifier; a phosphoric acid ester dispersant, wherein the dispersant isa polycaprolactone-modified methacrylate monophosphate; and afluorocopolymer.
 28. A dental restorative composition comprised of:afiller; a polymerizable acrylic monomer; a rheological modifier selectedfrom the group consisting of:(1) a hydroxyfunctional polycarboxylic acidamide according to the formula ##STR23## wherein the symbols have thefollowing meanings: R=aliphatic hydrocarbon groups having 6 to 60 carbonatoms, or aromatic hydrocarbon groups having 6 to 20 carbon atoms, oraliphatic or aliphatic/aromatic hydrocarbon radicals having 6 to 150carbon atoms which are interrupted by 2, 4, 6 or 8 carboxamide groups,or aliphatic hydrocarbon radicals having 4 to 150 carbon atoms which areinterrupted by 2 to 75 --O-- (oxygen) groups; R'=H, or C₁ to C₄ alkyl,or --Z'--(Q)_(y) --(OH)_(x) ; x=1 to 3; y=0 or 1; Z=an alkylene radicalhaving 2 to 6 carbon atoms; Z'=an alkylene radical which is identical toor different from Z, having 2 to 6 carbon atoms; Q=an aliphatichydrocarbon radical having 2 to 200 carbon atoms, which is linked via--O-- or ##STR24## to Z or Z' and is interrupted by zero to 99 oxygenatoms and/or carboxylic acid ester groups; and n=2to 3;and(2) thereaction product of:(a) from about 15 to 75 parts by weight of one ormore liquid polyalkoxylated nitrogen-containing compounds containingmore than one hydroxyl group and which also contain a pendant aliphaticradical of 6 to 40 carbon atoms selected from the group consisting oftertiary amines and amides of secondary amines; (b) from about 8 to 90parts by weight of one or more polycarboxylic acids; and (c) from about0.5 to 20 parts by weight of one or more liquid diamines of a weightaverage molecular weight of about 2000 or less,wherein the reaction iscontinued until the acid value is within the range of 5 to 14 and theamine value is within the range of 42 to 84; a dispersant selected fromthe group consisting of:(1) a phosphoric acid ester according to theformula ##STR25## wherein n=5 to 10 and m=1 to 20; and (2) a phosphoricacid ester according to the formula ##STR26## wherein R is a radicalselected from the group consisting of: oxyethyl methacryloyl-, oxyethylacryloyl-, polyoxypropyl methacryloyl-, glyceryl dimethacryloyl-, anddipentaerythritol pentaacryloyl-; and a fluorocopolymer of afluoroolefin, a cyclohexyl vinyl ether, an alkyl vinyl ether and ahydroxyalkyl vinyl ether, wherein the fluorocopolymer is comprised ofabout 40-60 mole percent fluoroolefin units, about 5-45 mole percentcyclohexyl vinyl ether units, about 5-45 mole percent alkyl vinyl etherunits and about 3-15 mole percent hydroxyalkyl vinyl ether units.
 29. Amethod of restoring a tooth comprising the steps of:preparing the toothfor restoration; and applying to the prepared tooth the dentalrestorative composite of claim
 6. 30. A method of restoring a toothcomprising the steps of:preparing the tooth for restoration; andapplying to the prepared tooth the dental restorative composite of claim17.
 31. A method of restoring a tooth comprising the steps of:preparingthe tooth for restoration; and applying to the prepared tooth the dentalrestorative composite of claim
 23. 32. A method of restoring a toothcomprising the steps of:preparing the tooth for restoration; andapplying to the prepared tooth the dental restorative composite of claim28.
 33. The dental restorative composition of claim 13, furthercomprising at least one of a rheological modifier and a fluorocopolymer,wherein said rheological modifier is present in an amount effective toreduce the volumetric shrinkage of the dental restorative duringpolymerization thereof, and wherein the fluorocopolymer is soluble in amethacrylate resin.
 34. The dental restorative composition of claim 17,further comprising at least one of a rheological modifier and afluorocopolymer, wherein said rheological modifier is present in anamount effective to reduce the volumetric shrinkage of the dentalrestorative during polymerization thereof, and wherein thefluorocopolymer is soluble in a methacrylate resin.